1. Field of the Invention
The invention relates in general to an automatic detection device for a frame header and a method thereof, and in particular, to a detection device and method for a DMB-TH communication protocol or PN signal mode in TDS OFDM systems.
2. Description of the Related Art
In DMB-TH systems, a data frame typically comprises a 4-layer structure, in which a basic frame is known as a signal frame, including a frame header and a frame body. In DMB-TH systems, the frame header comprises three modes: the frame header signal PN420 with a length of 420 symbols; the frame header signal PN595 with a length of 595 symbols; and the frame header signal PN945 with a length of 945 symbols. During signal transmission, the receiver determines the mode of the frame header of the signal frame, to accordingly perform different processing.
Conventionally, the method of determining the frame header mode is based on distance between two peaks generated by the cross correlation of the frame header sequence when frequencies of the transmitter and the receiver are synchronous.
However when a specific frequency offset occurs between the transmitter and the receiver, for example, frequency offset exceeding 30 KHz in the PN420 mode, and frequency offset exceeding 15 KHz in the PN945 mode, combining multipath effect and low signal to noise ratio (SNR), disturbance to the signal peaks for determining frame header mode renders inaccurate determinations.
As shown in FIG. 1(a), FIG. 1a illustrates the peak generation when the signals at the transmitter and receiver are synchronized, where the distance between two adjacent peaks 10a and 10b can be used to determine the header mode. Please refer to FIG. 1b, FIG. 1b illustrates the peak generation when a frequency difference exists between the signal frequencies at the transmitter and receiver and the peaks are unclear (12b), resulting in difficulty of frame header mode determination.
Thus, a need exists for an amplifier amplifying an input signal without introducing noise to the amplified signal.